Generally speaking, since the population is smaller in China you need to size up. A large shirt might fit a large person in China, but the American and European standard is bigger, so in these places it might be more of a medium.
This definitely far more likely than the opposite, sizing down. But there also many items that fit "true to size".
Most sellers have a size chart and you should definitely take the time to take your measurements and choose based on the size chart not the size you usually wear at home.
Reviews are also a great source to find out how different the size is to local retail.